Field of the Invention
The invention relates to a glazing comprising a glass substrate provided with a thin functional coating, the latter having transparency, electrical-conductivity and/or low emissivity properties.
It also relates to processes for obtaining such a glazing, more particularly with the aid of pyrolysis methods or methods using a vacuum.
This type of functional coating is more particularly used for equipping glazings to be used in buildings, coated with a low emissive coating, a glass substrate making it possible to reduce emission in the far infrared through the glazing of which it forms part from the inside to the outside of the room. By reducing energy losses partly due to said radiation escape, there is a significant improvement to the comfort of the persons located therein, particularly in winter. The thus covered substrate can be combined with another substrate by means of a layer of gas, the low emissive coating being located on the inside and in particular face 3 (counting from the outermost face) so as to form a highly effective, insulating double glazing.
These coatings can also be used on glazings to be employed in cars, as a result of their electrical conductivity properties, e.g. for forming heated glazings by providing current intakes.
Coatings of metal oxides having these properties are e.g. coatings of tin-doped indium oxide (ITO), zinc oxide doped with aluminium (ZnO:Al), with indium (ZnO:In), with tin (ZnO:Sn) or with fluorine (ZnO:F) or fluorine-doped tin oxide (SnO.sub.2 :F).
These metal oxide coatings can be obtained by different processes, such as vacuum processes (thermal evaporation, cathodic sputtering, optionally with the aid of a magnetron) or by the pyrolysis of metalorganic compounds projected by a vector gas in liquid, solid or gaseous form onto the surface of the glass substrate heated to a high temperature, but which is still below its softening point. The latter, contacted with a hot surface, decompose accompanied by oxidation in order to form a metal oxide coating thereon. The latter procedure is particularly advantageous to the extent that it makes it possible to envisage deposits directly on the ribbon of glass of a float-production line in a continuous manner.
However, for said coatings to reach a high performance level, particularly with respect to the emissivity and/or electrical conduction values, their thickness must be at least 180 nm, or beyond 400 nm and is usually between 300 and 450 nm.
However, when a thin coating has such characteristics, it gives the substrate which it coats an appearance in reflection on the "coating side", which may not be very highly appreciated from the esthetic standpoint.
Thus, for example, according to the teaching of EP-B-125 153, a fluorine-doped tin oxide coating SnO.sub.2 :F, whose limited thickness of 163 to 165 deposited on a 4 mm thick clear float glass substrate gives the latter a colouration in reflection in the blue, which is at present highly appreciated both in the building and car fields.
However, it has been found that a coating of the same nature, but in this case with a thickness of 360 nm, i.e. a coating with better performance characteristics, gives the same substrate an appearance in reflection on the coating side in the red-greenish range, i.e. a colouration which would be considered relatively unpleasing for the eye. Moreover, the coated substrate has a light reflection value R.sub.L on the coating side higher than 10 or 15% and a colour purity associated with said reflection which can exceed 10 to 15%, which means a definitely coloured and reflecting appearance of the substrate on the coating side (i.e. the side which is generally installed in face 3 of a double glazing installed in a building, i.e. that which is seen from the outside on viewing the facade. It is pointed out that the value of the purity indicates the intensity of the colour, the closer it is to 0%, the more it appears "whitewashed" and pastel. Therefore the colour is evaluated relative to the value of the light reflection R.sub.L.
However, the present tendency is towards a design of glazings, particularly those intended for buildings, which are not very reflecting, particularly when seen from the outside. The bright, reflecting appearance is even more prejudicial when associated with a not well appreciated tint.
Moreover, even if intrinsically a light reflection R.sub.L of approximately 15% is not great, it still signifies a certain drop in the transmitted solar energy quantity, particularly within the room and therefore reduces by a few percent the solar factor, i.e. the ratio of the sum of the transmitted solar energy and the solar energy absorbed by the glazing and reemitted towards the interior of the room to the incident solar energy. This is an energy disadvantage, particularly when it is wished to incorporate such a substrate into an insulating double glazing with a view to decreasing heating costs.
A first solution to this problem of appearance in reflection is provided by French patent application FR-A-2 684 095, whose teaching is incorporated into the present application. This solution firstly consists of interposing between the substrate and the aforementioned functional coating having a thickness of 200 to 400 mm, a first or inner covering, whose optical thickness is between 50 and 75 nm. On the coating is also provided a second or outer covering, whose optical thickness is approximately 1/4 of the average wavelength belonging to the visible range and preferably centred on 550 nm (the optical thickness being the product of the geometrical thickness by the refractive index of the covering in question).
The interest of such a stack is that there are two coverings on either side of the functional coating, which allows fine optimizations of their characteristics, essentially the optical and geometrical thicknesses and refractive index.
Such a combination of appropriately chosen coverings makes it possible to obtain monolithic substrates (e.g. of 4 mm thick float glass) which, once provided with the stack, have a light reflection R.sub.L of at the most 6%, accompanied by a colouration purity in reflection and normal incidence of at the most 3%. It also has an emissivity of at the most 0.2.
Installed in a double glazing in such a way that the coatings are in face 3, the latter has a slightly higher light reflection (but still remaining below 15%) with a colouration purity in reflection reduced still further in normal incidence and at the most 5%, even at the measurement incidence angle normally considered as unfavourable. Its solar factor in normal incidence reaches at least 0.76.
Such R.sub.L values firstly imply a suppression of most of the reflecting effect of the glazing, permitting an overall increase in the value of the energy transmission T.sub.E and therefore the solar factor.
With respect to the colouration purity values in reflection, in association with the R.sub.L values, they give the glazings, no matter whether they are monolithic or installed in double glazings, an only slightly intense coloured appearance, even by choosing an incidence angle which is generally not very favorable and which differs from the normal incidence. Thus, there is a better homogeneity of appearance of the glazings of a building facade seen from the outside.
However, it has not been envisaged to control and select the dominant wavelength in reflection on the "coating side", i.e. choose the colour in reflection, even if it is highly attenuated and whitewashed as a result of the combination of low purity and light reflection.
The aim of the invention is to develop a glazing, which optimizes this type of stack in order to retain all its advantages, whilst also being able to control the choice of colour in reflection, more particularly in order to be able to obtain a colour in reflection on the "coating side" in the blue range, which is considered to be highly desirable at present both in the building field and in the car field as being pleasing to the human eye.